Certain hydrofluoroolefins (HFOs), such as tetrafluoropropenes (including 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), and 1,3,3,3-tetrafluoro-1-propene (HFO-1234ze) are now known to be effective refrigerants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids. Unlike most chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), most HFOs pose no threat to the ozone layer. HFO-1234yf has also been shown to be a low global warming compound with low toxicity and, hence, can meet increasingly stringent requirements for refrigerants in mobile air conditioning. Accordingly, compositions containing these hydrofluoroolefins are among leading materials being developed for use in many of the aforementioned applications.
A manufacturing process for preparing one of the fluoroolefins, HFO-1234yf, is disclosed in U.S. Pat. No. 8,058,486, and uses 1,1,2,3-tetrachloropropene (HCO-1230xa) as starting raw material. The process consists of the following three steps: 1) HCO-1230xa+HF-->2-chloro-3,3,3-trifluoropropene (HCFO-1233xf)+HCl in a vapor phase reactor charged with a solid hydrofluorination catalyst such as fluorinated chromia, 2) HCFO-1233xf+HF-->2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) in a liquid phase reactor charged with a liquid hydrofluorination catalyst such as fluorinated SbCl5, and 3) HCFC-244bb-->HFO-1234yf in a vapor phase reactor.
The other fluoroolefins identified hereinabove are prepared similarly from different starting materials. Each of them is prepared from the dehydrochlorination of a hydrofluorocarbon, e.g. a fluoroalkane. More specifically, HFO-1234ze is formed from the dehydrochlorination of 1-chloro-3,3,3-trifluoropropane (244fa) in both the Z and E isomers. HFO-1233zd is prepared from the dehydrochlorination from 1,1-dichloro-3,3,3-trifluoro-1-propene (243fa) in both the Z and E isomers.
Unfortunately, this process for making fluoroolefin, e.g., HFO-1234yf, can lead to the generation of toxic and/or otherwise undesirable by-products, which are difficult to remove.
For example, one common method for removing impurities is via distillation. However, this method of removal is made difficult if the boiling point of the impurity is close to that of the final fluoroolefin products or if substance interactions bring otherwise dissimilar boiling compounds close together (for example azeotropes). Further, even after distillation, it is still possible that small quantities of undesirable impurities will remain.
As a result, there is a need to identify impurities generated in the process of making fluoroolefin, e.g., HFO-1234yf and methods for removing these impurities.